Regulations and computerized works have increased the demands for information memories for managing and saving all of electronic mails, data, and documents. One of the memories may be a storage system which has a plurality of storages being capable of handling a large amount of information and a storage management apparatus which reads or writes information with readiness from or to the storages and controls power supply to the storages. The storages in the storage system may preferably have large capacities such as hard disks. In this case, the hard disks are controlled so as to reduce power consumption by turning off motors at a standby state from the viewpoint of power saving. Upon detection of an access to a storage, the storage management apparatus turns on the motor of the accessed hard disk to start and thus returns to a normal operation.
The expression “turning off” a motor refers to an operation of stopping power supply for operations by the motor. The expression “turning on” a motor refers to a series of operations from a state that the motor has an off-state to a steady state.
Thus, for example, power supply units which supply power to the motors are desired to be capable of supplying power for turning on all motors for driving respective hard disks at the same time in consideration of the case desiring starting all hard disks at the same time. Since the power desired for turning on the motors is larger than the power desired at the steady state after the motors are turned on, the power supply units have been desired to be capable of supplying a large amount of power.
However, having such power supply units with a large power supply capability is disadvantageous from viewpoints of power saving, size reduction, and cost reduction.
On the other hand, when the amount of desired power for driving the hard disks exceeds the maximum power supply capability of the power supply unit, the hard disks may be divided into a plurality of groups, and the grouped hard disks may be started at different timings.
For example, one technology may calculate the maximum number of devices, which are simultaneously operable, based on the power supply requirement for the system and the power supply capability of the system and then start the calculated maximum number of devices. (Refer to Japanese Laid-open Patent Publication No. 2000-10678, for example).
Another technology has been proposed in which a plurality of disks are formed into some groups before power-on, the power is sequentially supplied to respective groups including disks which record/reproduce data in parallel, the power being supplied to each group for a time period desired for flow of starting current. (Refer to Japanese Laid-open Patent Publication No. 4-78062, for example).
Another technology has been proposed in which power is supplied for start-up to a part of a plurality of hard disks and supplied for a standby state to the rest of the hard disks. After the start-up of the part of the hard disks, the power desired for start-up is supplied to some of the rest of the hard disks. (Refer to Japanese Laid-open Patent Publication No. 2001-186655, for example).
Power saving processing in a storage system desires both of reduction of power consumption by hard disks and securing readiness for access. However, the method of dividing hard disks into a plurality of groups and starting the groups of hard disks at different times takes a long time until the start of entire access processing and may not sufficiently satisfying the readiness for requests for access.
The problem is not limited to hard disks but may occur in a storage system employing other types of storage.